As illustrated in FIG. 18, a steering apparatus for an automobile is constructed so that rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, and as the input shaft 3 rotates, a pair of left and right tie rods are pushed or pulled, which applies a steering angle to the front wheels of the automobile. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and this steering shaft 5 is inserted in the axial direction through a cylindrical shaped steering column 6, and is supported by the steering column so as to be able to rotate freely. The front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 by way of a universal joint 7, and the front end section for this intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9.
It has been conventionally possible to adjust the up-down position and the forward-backward position of the steering wheel 1 according to the size and driving posture of the driver. In order to enable the up-down position thereof to be adjusted, the front end section of the steering column 6 is supported by a vehicle body 11 via a horizontal shaft 10 so as to be able to pivotally displace. Moreover, a held bracket 12 that is fastened to a portion near the rear end side of the middle section of the steering column 6 is held between a pair of left and right holding plate sections 14 of a holding bracket 13 that is mounted on the vehicle body 11. A rod 15 that is inserted through this held bracket 12 is inserted through long holes 16 in the up-down direction that are formed in portions of the holding plate sections 14 that are aligned with each other. The up-down position of the steering wheel 1 can be adjusted within the range that the rod 15 is able to displace inside the long holes 16 in the up-down direction.
Moreover, in order to adjust the forward-backward position of the steering wheel 1, the steering shaft 5 and the steering column 6 are constructed so as to be able to extend and contract. The steering shaft 5 is constructed such that the rear end section of an inner shaft 17 on the front side and the front end section of an outer shaft 18 on the rear side are combined using a non-circular fit such as a spline fit so as to be able to transmit torque and to be able to displace in the axial direction. The steering column 6 is constructed such that the rear end section of an inner column 19 on the front side and the front end section of an outer column 20 on the rear side are combined and fitted together such that displacement is possible in the axial direction. Furthermore, long holes 21 in the forward-backward direction are formed in the held bracket 12 for inserting the rod 15 therein. The forward-backward position of the steering wheel 1 can be adjusted within the range that the rod 15 can displace inside the long holes 21 in the forward-backward direction.
The space between a head section 22 that is provided on the base end section of the rod 15 and a pressure piece 23 (see FIG. 5) that is fitted onto the tip end section of the rod 15 can be expanded or contracted by using an adjustment handle (not illustrated in the figure) that is attached to the rod 15 and a cam apparatus (not illustrated in the figure) that is operated by the adjustment handle. When the space between the head section 22 and the pressure piece 23 is expanded, it is possible to adjust the up-down position and the forward-backward position of the steering wheel 1. On the other hand, when the space between the head section 22 and the pressure piece 23 is contracted, the up-down position and the forward-backward position of the steering wheel 1 are held in the adjusted positions.
In order to keep down the cost for manufacturing an outer column provided with a held bracket of this kind of steering apparatus for vehicle, construction in which the held bracket and the outer column are formed integrally is effective. For example, JP 2002-249052 (A) discloses construction in which, as illustrated in FIG. 19 and FIG. 20, a pivot support bracket section 26, through which a horizontal shaft 10a for supporting the front end section of the steering column 6a by the vehicle body 11a so as to be able pivotally displace is inserted, is integrally formed with the steering column 6a. The pivot support bracket 26 is formed by hydroforming in which the metal tube of the steering column 6a is placed inside a mold, and part of this metal tube is caused to swell to match the inside shape of the mold by feeding a high-pressure fluid into the mold.
When applying this kind of hydroforming method to the integrated formation of the held bracket section to the middle section of the outer column in order to integrally form the held bracket and the outer column, preferably improvements in regards to the points (1) to (3) below.
(1) The thickness of the held bracket section that is formed by the hydroforming method is thin, and the strength and rigidity become low by that amount. Therefore, when the held bracket is firmly held between the pair of left and right holding plate sections of the holding bracket in order to maintain the adjusted position of the steering wheel, it becomes easy for the held bracket section to deform in a direction in which the width dimension thereof is reduced. When the held bracket has deformed, the support strength for supporting the outer column by the holding bracket decreases, and it becomes difficult to maintain the steering wheel in the adjusted position.
(2) The strength and rigidity of the held bracket section becomes low, so when an impact load is applied to the held bracket section during a collision accident, there is a possibility that the held bracket section will deform and the outer column will become unstable.
(3) The metal inside edges of the through holes that are formed in the held bracket section and the metal outer circumferential surface of the rod come in contact with each other. Therefore, when adjusting the forward-backward position of the steering wheel, the metal inside edges of the through holes and the metal outer circumferential surface rub or hit against each other, which causes vibration or abnormal sound that is unpleasant for the passengers and driver.